PolREFF Guide

Insulation of walls, roofs and floors

An energy efficient house should be warm and it should not lose heat. One of the best ways to prevent heat loss is insulating the walls and the roof. The walls lose 15-20% of total heat loss and the roof loses 10-15%. It is important to minimise these losses.


Types of insulation materials

Insulation materials are a significant element of the envelope of a modern building. They assure thermal and acoustic insulation.

Energy efficiency of insulation materials is measured by thermal conductivity coefficient λ which is calculated in Watts per metre per Kelvin degree [W/mK]. In general, a lower λ value indicates a more energy efficient material. The overall heat transfer coefficient (U-value) of the insulation depends on both the thermal conductivity of the material (λ) and its thickness. The U-value characterises the entire insulation. It is measured in Watts per square metre per Kelvin degree W/m2K. Well insulated walls have U = 0,25 and lower, well insulated roofs have a U of less than 0,20.

A wide range of insulation materials is available on the market:

•Mineral wool
• Expanded polystyrene
• Sandwich panels
• Expanded polystyrene covered with asphalt roofing
• Polyurethane foam
• Extruded polystyrene
• Mineral insulating materials
• Cellulose fibres

The infographics below present the use of most common insulation materials on individual elements of the house.


Effective thermal insulation of building partitions and roof

Element of the house


Recommended insulation material


The most effective way to insulate elements of the building that are in contact with the ground is to use the so-called perimeter insulation. It is an external, continuous insulation free of thermal bridges used for the building partitions that are in direct contact with the ground.

Installing thermal insulation on the external surfaces of basement walls eliminates the risk of freezing temperatures penetrating the walls and prevents moisture from condensing inside the building. The role of the peripheral insulation is not only to reduce heat loss but also to protect the external waterproofing from damage.

Extruded polystyrene plates
5 to 10 cm thick

Ground floors

In order to meet the thermal insulation standards the ground floor should be built as a layered construction: flooring, underlayer, appropriate insulating layers and base.

Before laying the floor it is important to remove about 30cm of the topsoil, and replace it with a 5 to 15 cm layer of sand or rubble. Then a 10 cm layer of concrete is poured followed by a 2.5 cm layer of waterproof cement or other hydro insulation. The thermal insulation goes on top.

The material has to be resistant to high pressure with good thermal insulation and hydrophobic properties. Boards of extruded polystyrene, polyurethane plates and concentrated LECA coated with cement about 1 cm thick are used for this purpose. A sheet of plastic sheeting is spread across the insulation. Not only does it separate and secure the layers but also provides lubrication for the base.

These types of floors require monolithic floor foundations
(eg. screeds out of concrete, cement, plaster etc.). Their role is to absorb all the tension that the floor is exposed to. The thickness of the base depends on the floor structure and the degree of compressibility of the insulation layer. The base should be separated from the vertical, solid building elements with a layer of tar-impregnated felt or other insulating material. This type of base is ideal for the final flooring.

Extruded polystyrene plates
3 to 5 cm thick

Polyurethane plates
5 cm thick

about 1 cm thick

Outside walls

Light wet method based on mineral wool and expanded polystyrene. Due to its low cost, good durability and simple installation this method is most commonly used to insulate exterior walls. It can be used to insulate walls made of bricks, airbricks, aerated concrete and concrete monolithic or prefabricated walls. Another convenient characteristic of this method is that the walls can be plastered or left unfinished.

Insulation using the light wet method is based on attaching the insulating material with glue and mounting pins to the exterior surface of the wall, covering it with a thin layer of mortar with a reinforcing mesh and finished with a layer of plaster. The basic insulating elements are mineral wool and expanded polystyrene. The exterior of the house must be insulated all the way up to the upper edges of the parapet or elbow walls. The lowest part of the insulation must be aligned with the top edges of the basement windows. The plinths must also be insulated.

It is also very important to insulate the exterior surface of window openings to prevent freezing and mould growth inside and around the frame.

10 to 25 cm thick

Mineral wool plates
10 to 25 cm thick


Ceilings between two residential floors or between the attic and the living space are most commonly insulated due to acoustic requirements and fire safety. In this case mineral wool provides soundproofing, slows down the spread of fire and reduces heat loss from rooms.

Mineral wool boards
5 to 15 cm thick


An uninsulated or poorly insulated roof can cause up to 10-15% of heat loss. This is why it is a crucial element for proper thermal insulation of a house. The type of insulation depends on the structure of the roof. Insulating a flat roof is different to insulating a pitched roof.

Key factors for insulating pitched roofs are:

• high thermal insulation, dependent on the thickness of the layer and thermal conductivity,
• high thermal insulation, dependent on the thickness of the layer and thermal conductivity, tightly sealed with no thermal bridges,
• the insulation material should fill the insulated surface tightly,
• effective protection against moisture,
• windproof in order to prevent infiltration of outside air and escape of warm air, while allowing moisture to pass through,
• fire resistant in order to create a barrier against spreading flames,
• good acoustic properties,
• easy to install.

It is important to remember that insulation puts additional pressure on the roof structure. This is why the insulation material must be light enough not to strain the existing structure and avoid the owner having to build an expensive, heavy structure.

Due to these requirements the best solution is glass wool. Not only is it warm but also very elastic which helps to seal the surface very tightly. Glass wool is very light so it doesn’t strain the roof structure. It is worth pointing out that in order to insulate an average 150 m2 pitched roof with glass wool, 450 kg of material is needed. Insulating the same roof with the lightest available mineral wool would require 900 kg of the material.

Hard mineral wool boards are used to insulate flat roofs. To insulate ventilated roofs the most commonly used materials are mats and granulates of mineral wool and sometimes boards.

Glass wool
layers 15 to 30 cm thick

Glass wool
layers 15 to 30 cm thick

Granules of mineral wool
15 to 35 cm thick

How much does it cost and how much can you save? A case study.


Thermal insulation of a residential building

Basic information

Key number

lnitial state

A 50 year old detached brick house with a a living area of 115 m2 is heated with a gas boiler. lts walls are 45 cm thick and have no insulation. Uninsulated walls and roof are responsible for huge heat losses in the autumn - winter period.

Annual costs of heating

7600 zł


The owner of the house contacted PolREFF engineers and decided:
1. to insulate external walls with styrofoam panels of 14 cm thickness and a thermal conductivity coefficient of 0,038 W/m2K. 

2. to insulate ceiling with a 30 cm thick layer of minerał ool and thermal conductivity coefficient of 0,052 W/m2K.

Cost of external walls insulation

18 000 zł

Cost of ceiling insulation

9000 zł


The investment will enable the owner and his family to enjoy amore comfortable home thanks to significantly reduced heat losses and to save zł 2.200 annually on energy costs.

Annual savings due to ower energy consumption

2200 zł

Brochure „Save energy and the environment”, FEWE